The present invention relates to a drawplate more particularly usable for the hot drawing or coupling of nickel, cobalt or titanium alloy sections, which can more particularly be used in jet aircraft engines.
Hot drawing processes are widely used for shaping metals or alloys, such as alloys of nickel or cobalt. In the case of these alloys, the temperatures required are generally high, being approximately 1000.degree. to 1350.degree. C. It is therefore necessary to use drawplates having good mechanical characteristics at these temperatures. Moreover, it is advantageous to be able to use the same drawplate for several drawing operations, whilst respecting the necessary dimensions with very small tolerances.
The drawplates used are generally constituted by a core hooped in a mount, the core e.g. being made from treated alloyed steel. Drawplates of this type can be suitable for obtaining articles having a circular cross-section, but also when it is wished to obtain refractory alloy sections with a complex shape, the hitherto used alloyed steel drawplates not making it possible to carry out several drawing operations under satisfactory conditions.
FIG. 1 is a vertical section of a drawplate according to the prior art. This drawplate is constituted by a core (1) hooped in a mount (3). In part, core (1) defines with mount (3) the drawing intake cone A, the core then defining the working cone B, the cylindrical bearing C and finally the mount defines the drawplate discharge channel D. The external shape of the upper part of the mount corresponds to that of the drawing container used which, in the present case is conical.
Such drawplates are not able to withstand high temperatures (of approximately 1150.degree. to 1250.degree. C.) and the high pressures (approximately 1300 MPa) necessary for shaping refractory cobalt or nickel alloys. Thus, during the drawing operation, the core (1) abuts against the mount (3) and the hooping stress is limited to the clamping force of the container, but the drawing force opposes said clamping force. Thus, it is difficult for the core to resist the drawing operation. Moreover, the upper end (1a) of the core in the drawplate intake cone cools rapidly, whereas the zone (1b) fitted into the mount constitutes a hot zone. Thus, breaking occurs in the drawplate due to thermal shocks.
French Pat. No. 2 497 126 discloses another type of drawplate, which is more particularly intended for drawing copper and aluminium alloys. This drawplate also comprises a joined core fitted into a mount, but the latter is formed from two components, which are arranged with a certain clearance from one another. However, such an arrangement does not make it possible to obtain the necessary resistance to high pressures and it is not suitable for the drawing and joint drawing of nickel, cobalt or titanium alloys.